Effect of ZrO2 nucleant on crystallisation behaviour, microstructure and magnetic properties of BaO-Fe2O3-B2O3-SiO2 glass ceramics

Differential thermal analysis, X-ray diffractometry and scanning electron microscopy with energy dispersive spectroscopy were used to study the crystallisation of glass ribbons with a composition of 35% BaO, 35% Fe2O3, 20% B2O3 and 10% SiO2 (mol%) with 1% ZrO2 added as a nucleant. The magnetic properties of ribbons prepared via cooling the melts between steel rollers were measured with a vibrating sample magnetometer. The addition of ZrO2 apparently resulted in a quite distinct glass-in glass phase separation in as prepared specimens, greatly affecting the nucleation process. Heat treatment of specimens at their DTA exo-peak temperature of 721 degrees C led to the formation of BaFe12O19 and BaB2O4 as the only crystalline phases. The glass ribbons heat treated in one-stage exhibited a quite non-uniform distribution of particles exhibiting exaggerated grain growth, while a two-stage heat treatment at 526 and 721 degrees C for different time periods generally led to more uniform distribution of platelet particles. The values of saturation magnetisation of specimens were in the M-s = 23-29 emu/g range, while the coercivity values varied between H-g = 1800-3000 Oe. (C) 2006 Elsevier Ltd and Techna Group S.r.l. All rights reserved.